Chengdao Li

Hiroyuki Nonogaki

Jose M. Barrero

Frontiers in Plant Science

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Editorial: Seed Dormancy, Germination, and Pre-harvest Sprouting

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EDITORIALpublished: 30 November 2018doi: 10.3389/fpls.2018.01783Frontiers in Plant Science | www.frontiersin.org 1 November 2018 | Volume 9 | Article 1783Edited and reviewed by:Alma Balestrazzi,University of Pavia, Italy*Correspondence:Chengdao Lic.li@murdoch.edu.auSpecialty section:This article was submitted toPlant Breeding,a section of the journalFrontiers in Plant ScienceReceived: 02 October 2018Accepted: 16 November 2018Published: 30 November 2018Citation:Nonogaki H, Barrero JM and Li C(2018) Editorial: Seed Dormancy,Germination, and Pre-harvestSprouting. Front. Plant Sci. 9:1783.doi: 10.3389/fpls.2018.01783Editorial: Seed Dormancy,Germination, and Pre-harvestSproutingHiroyuki Nonogaki 1, Jose M. Barrero 2 and Chengdao Li 3*1Department of Horticulture, Oregon State University, Corvallis, OR, United States, 2Commonwealth Scientific and IndustrialResearch Organisation, Agriculture and Food, Canberra, ACT, Australia, 3Western Barley Genetics Alliance, MurdochUniversity, Murdoch, WA, AustraliaKeywords: dormancy, seed germination, pre-harvest sprouting, late maturity alpha-amylase, functional genes,QTLEditorial on the Research TopicSeed Dormancy, Germination and Pre-harvest SproutingSeed germination is the first critical step of the plant life cycle and the foundation of agriculturalproduction. In contrast, seed dormancy prevents seedling emergence in a wrong season or placein wild species. In cereal crops, the lack of dormancy results in pre-harvest sprouting (PHS) underparticular conditions of humidity and temperature, which triggers reserve mobilization, mainlystarch degradation by α-amylase (Bewley et al., 2013), and reduces grain quality. Annual lossesfrom PHS are likely to approach $1 billion U.S. dollars worldwide (Black et al., 2006).International Symposium on Pre-harvest Sprouting in Cereals gathered scientists investigatingseed dormancy and PHS and staged an excellent opportunity for discussion between basic andapplied researchers for the common goal-PHS prevention. This Research Topic: Seed Dormancy,Germination, and Pre-harvest Sprouting collected full papers and abstracts from the symposiumand also other highly relevant papers submitted to the Journal. The collection also covers anothergrain quality defect that is often confounded with PHS: Late Maturity α-Amylase (LMA). ThisResearch Topic serves as a reference book for PHS and LMA, in addition to the previous reviewsfor LMA and PHS (Mares and Mrva, 2014; Rodríguez et al., 2015).Seed germination is promoted by GA. One way to prevent PHS is to understand themechanisms of germination promotion by GA and block that pathway. Nelson et al. compared thetranscriptomics of the sleepy1-2 (sly1-2), a GA signaling mutant, and wild-type seeds and founddormancy-promoting stored transcripts. Mutations in these genes weaken seed dormancy andtherefore their enhancement has potential to prevent PHS.Another approach to strengthen seed dormancy is to reinforce ABA metabolism or signaling.Nonogaki and Nonogaki enhanced expression of nine-cis-epoxycarotenoid dioxygenase (NCED)and caused hyperdormancy. While the proof of concept was tested in Arabidopsis, the geneconstruct was created using a sorghum NCED and a wheat promoter. Therefore, the genetic tool isready for direct translation into crops. FUSCA3 (FUS3) enhances ABA biosynthesis in Arabidopsis(Gazzarrini et al., 2004). Sun et al. has found that Triticum aestivum FUS3 (TaFUS3) interacts withTaSPA (STORAGE PROTEIN ACTIVATOR) (Albani et al., 1997). While the TaFUS3 analysis wasnot performed in the context of direct regulation of NCED expression, the interaction of TaFUS3and TaSPA to transactivate gene expression advanced our understanding of the FUS3 function inABA regulation.ABI5 is involved in ABA signaling in seeds and regulated by nitric oxide (NO) (Nonogaki, 2017).Signorelli and Considine provided their perspectives about the action of reactive nitrogen speciesNonogaki et al. Seed Dormancy and Pre-harvest Sproutingand the free radicals with an emphasis on post-translationalmodification. Understanding this pathway is also critical forPHS prevention and potentially more important for seedgermination recovery from PHS-resistant crops because NOpromotes germination.The progresses in basic science are now ready to be translatedinto crops. However, the fundamental mechanism may havediversified among various crops. Therefore, species-specific casestudies are also necessary. Das et al. performed metabolomicanalysis using PHS-susceptible and -resistant wheat grains andpresented significant differences in small molecule profiles. Theseprofiles, together with proteomic and transcriptomic profiles,will identify crop-specific responses that might not be foundin Arabidopsis. Benech-Arnold and Rodriguez shared theirexperience in PHS research in sorghum. While they also founda GA-ABA balance as the core mechanism of dormancy, GAdeactivation, rather than ABA biosynthesis, turned out to bea critical factor for PHS resistance in sorghum. Their findingexemplifies the importance of comparative analyses betweenspecies. New QTL analyses in other crops offer a basis for cloningnovel genes. Li et al. identified 43 QTL associated with lowtemperature seed germination of maize while Lee et al. identified39 candidate SNPs for PHS by re-sequencing 21 representativeaccessions of rice. These new loci in maize and rice couldpotentially shed light on hidden pathways of seed dormancyand PHS. In the past, the rice QTL analysis for PHS identifiedSeed dormancy 4 (Sdr4), which was not found from Arabidopsis(Sugimoto et al., 2010). Likewise, the analysis of the barleyQsd1 identified the critical role of alanine aminotransferase inseed dormancy regulation through a yet-unknown pathway (Satoet al., 2016). Thus, more discoveries are anticipated from the cropQTL analyses.This Research Topic also addresses inter- and intraspeciesdifferences in dormancy and PHS mechanisms by using wild,local or synthetic species. Nakamura et al. crossed the wild barleyto a malting barley and highlighted the importance of maternaleffects. Dale et al. crossed Aegilops tauschii with a hexaploidPHS-susceptible white-grain wheat and generated a syntheticoctaploid wheat. By using the advanced backcross population,they identified dormancy-associated QTLs. In addition to wildor synthetic species, it is also important to use varieties of localorigin for addressing geographical and climate differences of PHSresponses in a global scale. Sydenham and Barnard conductedQTL analysis of the South African wheat cultivars while Zhouet al. performed genome-wide association study of the largegermplasm collection of Chinese landraces.The ultimate goal of PHS research is to secure grain quality.Zhang and Li employed genomic approaches to compare α-amylase genes in cereals, including promoters. The informationis a great resource to understand the “behavior” of thestarch-degrading enzyme and regulate its expression for grainquality. Unusual α-amylase activity in late maturing wheatgrains, so-called LMA, is a genetic defect and considered anegative trait for grain quality. However, Newberry et al. arenow raising question about the traditional view about LMA.They observed little correlation between LMA and the endproduct functionality and concluded that LMA has limitedimpact on bread baking. Martinez et al. even demonstratedinconsistency between some falling number and PHS traits.These new discoveries could be a game changer in breedingprograms.Finally, another important aspect of PHS studies is the synergybetween basic and applied science. As discussed for Sdr4 andQsd1, crop research revealed the presence of novel pathwaysof seed dormancy, which was not known in model species.The mitogen-activated protein kinase kinase 3(TaMKK3) isemerging as a novel seed dormancy regulator in crops (Nakamuraet al., 2016; Torada et al., 2016). Shorinola et al. analyzeda causal relation between TaMKK3 and PHS in the globalgermplasm and confirmed its significance for seed dormancy.TaMKK3 also offers a new target pathway to be investigatedin basic seed dormancy research using Arabidopsis. Thus, PHSstudies are advancing both basic seed biology and applied cropscience.AUTHOR CONTRIBUTIONSAll authors listed have made a substantial, direct and intellectualcontribution to the work, and approved it for publication.FUNDINGThe project is partially supported by the Grain Research andDevelopment Corporation for CL (UMU00046).REFERENCESAlbani, D., Hammond-Kosack,M. C., Smith, C., Conlan, S., Colot, V., Holdsworth,M., et al. (1997). The wheat transcriptional activator SPA: a seed-specific bZIPprotein that recognizes the GCN4-like motif in the bifactorial endosperm boxof prolamin genes. Plant Cell 9, 171–184. doi: 10.1105/tpc.9.2.171Bewley, J. D., Bradford, K. J., Hilhorst, H. W. M., and Nonogaki, H. (2013).Seeds: Physiology of Development, Germination and Dormancy. New York, NY:Springer.Black, M., Bewley, J. D., and Halmer, P. (2006). Encyclopedia of Seeds-Science,Technology and Uses. Wallingford: CABI.Gazzarrini, S., Tsuchiya, Y., Lumba, S., Okamoto, M., and McCourt,P. (2004). The transcription factor FUSCA3 controls developmentaltiming in Arabidopsis through the hormones gibberellin andabscisic acid. Dev. Cell 7, 373–385. doi: 10.1016/j.devcel.2004.06.017Mares, D. J., and Mrva, K. (2014). Wheat grain preharvest sprouting and latematurity alpha-amylase. Planta 240, 1167–1168. doi: 10.1007/s00425-014-2172-5Nakamura, S., Pourkheirandish, M., Morishige, H., Kubo, Y., Nakamura,M., Ichimura, K., et al. (2016). Mitogen-activated protein kinasekinase 3 regulates seed dormancy in barley. Curr. Biol. 26, 775–781.doi: 10.1016/j.cub.2016.01.024Nonogaki, H. (2017). Seed biology updates–Highlights and new discoveriesin seed dormancy and germination research. Front. Plant Sci. 8:524.doi: 10.3389/fpls.2017.00524Frontiers in Plant Science | www.frontiersin.org 2 November 2018 | Volume 9 | Article 1783Nonogaki et al. Seed Dormancy and Pre-harvest SproutingRodríguez, M. V., Barrero, J. M., Corbineau, F., Gubler, F., and Benech-Arnold, R. L. (2015). Dormancy in cereals (not too much, not solittle): about the mechanisms behind this trait. Seed Sci. Res. 25, 99–119.doi: 10.1017/S0960258515000021Sato, K., Yamane, M., Yamaji, N., Kanamori, H., Tagiri, A., Schwerdt, J. G.,et al. (2016). Alanine aminotransferase controls seed dormancy in barley. Nat.Commun. 7:11625. doi: 10.1038/ncomms11625Sugimoto, K., Takeuchi, Y., Ebana, K., Miyao, A., Hirochika, H.,Hara, N., et al. (2010). Molecular cloning of Sdr4, a regulatorinvolved in seed dormancy and domestication of rice. Proc.Natl. Acad. Sci. U.S.A. 107, 5792–5797. doi: 10.1073/pnas.0911965107Torada, A., Koike, M., Ogawa, T., Takenouchi, Y., Tadamura, K., Wu, J., et al.(2016). A causal gene for seed dormancy on wheat chromosome 4A encodesa MAP kinase kinase. Curr. Biol. 26, 782–787. doi: 10.1016/j.cub.2016.01.063Conflict of Interest Statement: The authors declare that the research wasconducted in the absence of any commercial or financial relationships that couldbe construed as a potential conflict of interest.Copyright © 2018 Nonogaki, Barrero and Li. This is an open-access articledistributed under the terms of the Creative Commons Attribution License (CC BY).The use, distribution or reproduction in other forums is permitted, provided theoriginal author(s) and the copyright owner(s) are credited and that the originalpublication in this journal is cited, in accordance with accepted academic practice.No use, distribution or reproduction is permitted which does not comply with theseterms.Frontiers in Plant Science | www.frontiersin.org 3 November 2018 | Volume 9 | Article 1783

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Editorial: Seed Dormancy, Germination, and Pre-harvest Sprouting

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